Crustal structure of the Indus–Tsangpo suture zone and its ophiolites in southern Tibet

Abstract

The >2000-km-long Indus–Tsangpo suture zone (ITSZ) in southern Tibet contains remnants of Neotethyan oceanic lithosphere, ophiolitic mélanges, flysch units and continental rocks, and has been interpreted as the boundary between the India and Eurasia plates. We have used field-based structural analyses and geological mapping in five key ophiolite massifs (Luobusa, Zedang, Xigaze, Jiding and Dongbo) and petrofabric studies of core samples recovered through the Luobusa Scientific Drilling Project to document the structural architecture and the deformation history of the ITSZ. The structural and kinematic analyses of the suture zone units indicate the occurrence of superposed deformation fabrics, which developed first during the ophiolite emplacement and then during the subsequent India–Asia continental collision. The suprasubduction zone ophiolites were emplaced southward onto the northern margin of the proto-Indian plate in the late Cretaceous. The continental collision between the ophiolite-laden proto-Indian margin and the Lhasa terrane of the Eurasian plate in the early Paleogene resulted in backthrusting and inversion of the structural order of the ITSZ. The ophiolite massifs, ophiolitic mélanges and flysch units were thrust northward as nappe sheets over the Eocene and younger forearc basin strata. The ITSZ shows, therefore, a complex structural anatomy characterized by both south and north-directed thrust faults, and ductile and brittle deformation fabrics.